<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>CSS垂直居中</title>
    <style>
        .wrapper{
            width: 500px;
            height: 500px;
            background-color: pink;
            display:flex;
            text-align:center;
            flex-flow:column;
            justify-content:flex-start;
        }

        .box{
            width: 100px;
            height: 100px;
            background-color: deepskyblue;            
        }

        .help{
        width: 100px;
        height: 100px;
        flex-grow: 1;
        background-color:orangered;
        }
    </style>
</head>
<body>
<div class="wrapper">
    <div class="box"></div>
    <div class="help"></div>
</div>
</body>
</html>